1. Field of the Invention
The present invention relates to a pattern formation with a light and radiation sensitive a negative type resist which is utilized for a preparation of semiconductors, super conductive Josephson devices, elastic surface wave devices etc.
2. Description of the Prior Art
As the etching step in the production of semiconductor integrated circuits, a process for forming an etched pattern by using a light sensitive resin which is sensitive to visible ray and ultraviolet ray (photoresist) has been practically employed.
The photoresists are classified into positive and negative photoresists. The positive photoresists are decomposed in polymer chain by light to be soluble in a solvent and can be a mixture of a phenol type polymer and a diazoquinone derivative. On the other hand, the negative photoresists are crosslinked in molecular chains by light to be insolubilized to a solvent and can be a mixture of a cinnamic acid derivative, a bisazido derivative and a rubber type resist material such as natural rubber, polyisoprene and polybutadiene in a cyclic form. Recently, requirements of higher density and higher integration of devices have been increased to improve reliability and characteristics of the integrated circuits. Thus, special studies for development of ultrafine work technology for circuit patterns have been made. In the studies, a process for forming a circuit pattern having high accuracy by exposure of high energy radiation such as far ultraviolet rays having short wavelength, X ray and electron bean instead of visible light has been developed. The process has been practically employed for a preparation of a circuit pattern mask. The process for producing a high density integrated circuit comprises a step of producing a mask by a radiation drawing process and a step of printing a circuit pattern of the mask on a silicon substrate. In the step of production of the mask, a radiation sensitive polymer is used as a resist. In the printing step, the conventional photoresist has been used. In both steps, a resist material is coated on a substrate to form a film and is exposed by the radiation or light and is developed to form a fine pattern and then, the layer having the fine pattern on the board is etched to remain the pattern forming part. In the step of the production of the integrated circuit, high sensitivity and high resolution are important as functional characteristics required for the resist. A resist corresponding to fine work accuracy upto 1 .mu.m as the resolution is especially required, in view of severer requirement for higher density of an integrated circuit.
In the etching step, a dry etching process by a gas plasma or a reaction sputtering has been newly employed instead of a wet etching process. Thus, excellent resist durable to the dry etching is required. Certain radiation sensitive resist used for the production of the mask have been proposed. It is quite small to satisfy with all of the above-mentioned requirements. For example, epoxy 1,4-polybutadiene has been known as the negative type resist and it has high sensitivity in the order of 10.sup.-7 C/cm.sup.2 but has unsatisfactory resolution. On the other hand, said rubber type negative type resist has been mainly utilized as a photoresist used in a printing process. Such resist has high sensitivity but has not satisfactory resolution. In a practical application, the accuracy for about 3 .mu.m has been limit. It has been difficult for using it in a production of an integrated circuit having high integration which requires higher accuracy.